Long only 1/n portfolio#

import pandas as pd
pd.options.plotting.backend = "plotly"

import yfinance as yf

from cvx.simulator.builder import builder
from cvx.simulator.grid import resample_index
data = yf.download(tickers = "SPY AAPL GOOG MSFT",  # list of tickers
                   period = "10y",                   # time period
                   interval = "1d",                 # trading interval
                   prepost = False,                 # download pre/post market hours data?
                   repair = True)                   # repair obvious price errors e.g. 100x?
[                       0%%                      ]
[**********************50%%                      ]  2 of 4 completed
[**********************75%%**********            ]  3 of 4 completed
[*********************100%%**********************]  4 of 4 completed

prices = data["Adj Close"]
capital = 1e6
b = builder(prices=prices, initial_cash=capital)

for time, state in b:
    # each day we invest a quarter of the capital in the assets
    b[time[-1]] = 0.25 * state.nav / state.prices
portfolio = b.build()
portfolio.profit.cumsum().plot()
portfolio.nav.plot()

Rebalancing#

Usually we would not execute on a daily basis but rather rebalance every week, month or quarter. There are two approaches to deal with this problem in cvxsimulator.

  • Resample the existing daily portfolio (helpful to see effect of your hesitated trading)

  • Trade only on days that are within a predefined grid (most flexible if you have a rather irregular grid)

Resample an existing portfolio#

portfolio_resampled = portfolio.resample(rule="M")
frame = pd.DataFrame({"original": portfolio.nav, "monthly": portfolio_resampled.nav})
frame
original monthly
Date
2013-11-18 1.000000e+06 1.000000e+06
2013-11-19 9.971421e+05 9.971421e+05
2013-11-20 9.957835e+05 9.957705e+05
2013-11-21 1.005772e+06 1.005754e+06
2013-11-22 1.006996e+06 1.006984e+06
... ... ...
2023-11-13 7.296839e+06 7.277763e+06
2023-11-14 7.400583e+06 7.381357e+06
2023-11-15 7.423856e+06 7.404585e+06
2023-11-16 7.507114e+06 7.487891e+06
2023-11-17 7.453904e+06 7.434391e+06

2518 rows × 2 columns

print(portfolio_resampled.stocks)
                    AAPL          GOOG         MSFT          SPY
Date                                                            
2013-11-18  15395.488405   9730.485911  8041.498826  1671.757412
2013-11-19  15395.488405   9730.485911  8041.498826  1671.757412
2013-11-20  15395.488405   9730.485911  8041.498826  1671.757412
2013-11-21  15395.488405   9730.485911  8041.498826  1671.757412
2013-11-22  15395.488405   9730.485911  8041.498826  1671.757412
...                  ...           ...          ...          ...
2023-11-13   9969.967548  13578.374022  5015.485110  4098.313431
2023-11-14   9969.967548  13578.374022  5015.485110  4098.313431
2023-11-15   9969.967548  13578.374022  5015.485110  4098.313431
2023-11-16   9969.967548  13578.374022  5015.485110  4098.313431
2023-11-17   9969.967548  13578.374022  5015.485110  4098.313431

[2518 rows x 4 columns]
# almost hard to see that difference between the original and resampled portfolio
frame.plot()
# number of shares traded
portfolio_resampled.trades_stocks.iloc[1:].plot()

Trade only days in predefined grid#

b = builder(prices=prices, initial_cash=capital)

# define a grid
grid = resample_index(prices.index, rule="M")

for time, state in b:
    # each day we invest a quarter of the capital in the assets
    if time[-1] in grid:
        b[time[-1]] = 0.25 * state.nav / state.prices
    else:
        # forward fill an existing position
        b[time[-1]] = b[time[-2]]
        
portfolio = b.build()
portfolio.nav.plot()
# Trading only once a month can lead to days where 150k had to be reallocated
portfolio.turnover.iloc[1:].plot()

Why not resampling the prices?#

I don’t believe in bringing the prices to a monthly grid. This would render it hard to construct signals given the sparse grid. We stay on a daily grid and trade once a month.